| Characteristics of hormones | - Glands secrete hormone directly into the blood
- Carried in the blood plasma to target cells, which have specific receptors on the cell-surface membranes that are complementary to a specific hormone |
| Second messenger model | - One mechanism of hormone action
- This mechanism is used by 2 hormones involved in the regulation of blood glucose conc., namely adrenaline + glucagon |
| Mechanism involving adrenaline (1) | - Adrenaline binds to receptor on cell-surface membrane of a liver cell
- Causes the protein to change shape |
| Mechanism involving adrenaline (3) | - Leads to the activation of an enzyme called adenyl cyclase
- Converts ATP to cAMP |
| Mechanism involving adrenaline (4) | - cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape + therefore activating it |
| Mechanism involving adrenaline (5) | - Protein kinase enzyme catalyses the conversion of glycogen to glucose
- Moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins |
| Role of the pancreas in regulating blood glucose | - Gland behind stomach
- Produces enzymes (protease, amaylase, lipase) for digestion
- Hormones (insulin, glucagon) for regulating blood glucose conc.
- Groups of hormone-producing cells known as islets of Langerhans |
| What do the cells of islets of Langerhans include | - alpha cells, which are larger, produce glucagon hormone
- beta cells, which are smaller, produce insulin hormone |
| The role of the liver in regulating blood sugar | - Made up of cells called hepatocytes
- Regulates blood glucose conc.
- While the pancreas produces hormones insulin and glucagon, it is in the liver where they have their effects |
| 3 important processes associated with regulating blood sugar in the liver | - Glycogenesis
- Glycogenolysis
- Gluconeogenesis |
| Glycogenesis | - Conversion of glucose into glycogen
- When blood glucose conc. is higher than normal the liver removes glucose form the blood, converts it to glycogen |
| Glycogenolysis | - Breakdown of glycogen to glucose
- When blood glucose conc. is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose conc. |
| Gluconeogenesis | - Production of glucose from sources other than carbs
- When its supply of glycogen is exhausted, the liver can produce glucose from non-carb sources such as glycerol + amino acids |
| Regulation of blood glucose concentration | - If conc. too low, cells will be deprived of energy + die
- Brain cells are especially sensitive as can only respire glucose
- If conc.too high, lowers water potential of blood, dehydration |
| Factors that influence blood glucose concentration, the 3 sources of glucose | - Diet - food
- Glycogenolysis
- Gluconeogenesis |
| How does glucagon work? | - Binds to complementary receptors on target cells
- Activates cAMP (secondary messenger)
- This activates phosphorylase
- Hydrolyses glycogen to glucose (glycogenolysis) |
| How does insulin work? | - Insulin increases muscle and liver cells permeability to glucose
- Increases rate of diffusion into cells |
| Adrenaline | - Similar effect to glucagon
- Released in times of stress
- Glycogen to glucose
- Prevents glycogen formation |
| Diabetes | - A disease signified by high blood sugar
- The symptoms can include, excessive urination, thirst and tiredness |
| Type 1 | - Due to an autoimmune response
- Beta cells are destoryed, therefore body cannot produce insulin
- Controlled by injecting insulin |
| Type 2 | - Due to age or obesity
- Insiulin is prevened from binding to receptors on cell membrane
- Protein receptor changes shape
- Controlled with diet or/and exercise |
| Negative feedback | - Only when the blood glucose concentration falls below the set point is insulin secretion reduced (negative feedback), leading to a rise in blood glucose concentration
- In the same way, only when the concentration exceeds the set point is glucagon secretion reduced (negative feedback), causing a fall in the blood glucose concentration |
| Example - after a meal | - Increases blood glucose
Negative feedback - back to here
- B cells detect + secrete insulin
- Increase cells permability to glucose
- Glucose diffuses into muscle cells + liver cells
- Used in respiration, converted into glyocgen, converted into lipid synthesis
- Decreases blood glucose to norm |
| Example - fasting | - Decreases blood glucose
- Sensed by alpha cells
Negative feedback - back to here
- Glucagon
- Hydrolyse glycogen - glucose
- Lipids/amino acids - glucose
- Increases blood glucose to norm |
